text:
Why does the FAA place such emphasis on runway incursions in the test standards?
In the FAA's ACS and the PTS there are many references to preventing runway incursions. In the test standards one will find it is elevated to becoming a special emphasis area and within the CFI PTS, the mandatory runway incursion task is the longest and wordiest task. So clearly runway incursions is a special subject for the FAA.
I understand the safety importance of this, but what strikes me as odd is it seems there is too much emphasis on this subject. Most of the mentions are added as revisions of the text. Reading between the lines, did something like a specific incident cause these additions? Was there an emerging runway incursion trend that prompted this?

This is borderline opinion based for me as I don't think anyone would be able to say with certainty why the FAA adds specific questions to their tests. The worst fatal accident in history, the Tenerife Airport Disaster, was caused by a runway collision, and there have been others. So it's definitely on people's minds.

Re: “did a specific incident cause these additions?” That’s not uncommon. It’s sometimes said that “the regulations are written in blood”, so it’s very well possible that someone did something so ignorant that a regulation or test question was created to address it.

According to what I can piece together from various FAA sources, the FAA determined in 2007 that there were an unacceptable number of incursions and they launched a program to address them. Although the number of incursions did indeed drop, they later started increasing again. Presumably the FAA doesn't believe that the number of runway incursions is consistently low enough to 'relax' the emphasis on them.

2010 press release:

In 2007, after 25 serious incursions, the FAA launched a Call to
Action with aviation leaders from airlines, airports, air traffic
control and pilot unions, and aerospace manufacturers to address
runway safety issues.

2008 report:

In August 2007, we met with more than 40 aviation leaders from
airlines, airports, air traffic controller and pilot unions, and
aerospace manufacturers under a “Call to Action” for Runway Safety.
Together, we developed an ambitious plan focused on cockpit and air
traffic procedures, training, increased awareness, runway/ taxiway
layout, signage and markings, and the timely development and
implementation of new technology.

2011 SAFO:

In August 2007 the Federal Aviation Administration (FAA) Administrator
issued a “Call to Action” on runway safety. This included an internal
challenge to the FAA to reduce runway incursions by 10% in five years
ending in 2013. After the 2007 “Call to Action,” runway incursions
involving pilots steadily decreased, however, as time has passed the
trend has reversed.

2015 report:

Since this time, Category A and B runway incursions, events that
represent the highest risk of a collision, have dropped by 44 percent
since the last C2A. Seven years have passed since the last runway
collision at a major airport and nine years since the last fatal
runway collision. Despite this long standing trend, A and B events
have recently begun to increase.

what a great answer.

Off the top of my head (have no stats at hand, too lasy to google), runway incursions are not very common, but considering the aforementioned efforts to prevent them, they are obviously way too common.
Runway incursion is an event with very possible and likely catastrophic consequenses, since should a collision be imminent after touchdown or during takeoff roll there is pretty much nothing either party can do. The one rolling on the runway has too much energy to stop quickly, or too little to lift off, and the one crossing or turning onto the runway cannot get out of the way due to slow speed and limited capability to accelerate.
The prudence of FAA is, of course, mostly aimed at high capacity/high traffic airports, where safety implications are obvious and very critical. In these cases the incursions also cause, in their less dangerous form, unnecessary load on traffic management in form of go arounds, and take up controller focus and time, possibly escalating to other more or less troublesome situations.

Just for information, in the US there were over 1200 runway incursions in the 2020 financial year: https://www.faa.gov/airports/runway_safety/statistics/year/?fy1=2021&fy2=2020

Oh, that is quite many... what do the OI, PD and VPD stand for?

type of surface events (operational incident [OI], pilot deviation [PD], and vehicle pedestrian deviation [VPD])


text:
What is "ACO transition"?
In MSFS2020, I frequently hear terms like "Cleared to ACO transition" and I can set an ACO in my flight plan.  What exactly is an ACO and its obviously not a unique point because they seem to be everywhere?
It was for KCAK (Akron-Canton Regional Airport) but I thought I saw the same thing for KCLE as well, maybe I was mistaken. But the MSF2020 ATC says ACO transition.

Welcome to aviation.SE! Do you have a specific location where this took place? If so, that's helpful.

In general, a transition is an optional portion of a Standard Terminal Arrival (STAR) or Standard Instrument Departure (SID). You might hear "Cleared to the XYZ airport via the ABC Four Departure, DEF transition, then as filed" where the ABC4 departure procedure includes one possible routing that terminates at DEF. Note that three-letter fixes denote VORs/VORTACs and would be pronounced on the radio as their full name (e.g. "ACO" is the "Akron" VOR-DME). I am not familiar with the term "ACO transition" as a separate defined thing.

As a matter of fact it WAS for KCAK but I thought I saw the same thing for KCLE as well, maybe I was mistaken.  But the MSF2020 ATC says ACO transition - I'll investigate further.  Thanks.

A transition is a branch of a Standard Terminal Arrival Route (STAR) or a Standard Instrument Departure (SID). ACO is the identifier for the Akron VOR/DME, which is a a navaid. It’s not surprising then that you would hear of an ACO transition for both KCAK and KCLE.
I would provide a chart showing where these are, but I can’t find any plates for the older VOR navigation. All the ones I find are RNAV which use GPS rather than navaids. Although the ACO VOR/DME is still operational, they are slowly being decommissioned. The FAA may have eliminated the VOR SIDS and STARs and are now only using the RNAV routes. It’s likely that the sim is using outdated plates.
If you are unfamiliar with SIDs and STARs you can check out This question.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


text:
What is this airplane seen over Delhi?
It was flying over Delhi, India 6:41PM IST May 22 2021

This immediately says "Soviet design space"

Awesome David! I saw it, thought to myself I don't know what model this is, but it's an Ilyushin, and then saw your comment ... scrolled down, Il-76. Amazing how clearly that form language announces itself!

Isn’t this design also similar to some planes from the Royal Air Force? I ran Google Lens on this image, and it suggested an RAF plane right off the bat.

Sort of. It has the same basic form as the C-17 and A400M (t-tail, high wing, 4 engines), but other than this characteristics it’s pretty different.

That is a Silk Way Airlines Ilyushin Il-76. Here is a snapshot from flightradar24 from 13:03 UTC (6:33 PM IST) where the aircraft is approaching Delhi Airport:

Thanks a lot kind stranger!

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Why do helicopters not flip when using cyclic pitch control to move?
Let's say a helicopter wants to move forward. To do so, cyclic pitch is applied to the blades 90 degrees off which applies a torque on the blades to tilt the craft forward. Once the helicopter is tilted there is now lift upwards and lift forward. But why doesn't the helicopter just keep tilting forward, doing flips?
My first thought was that the pilot only applies the torque until they are satisfied with the tilt angle then returns to normal control. But this can't be the case since in many videos I've seen the swash plate remains tilted throughout the entirety of the movement. I can't think of another way that the helicopter could remain at the desired forward angle and not just flip repeatedly.

Perhaps the really good answer to this question answers your question? https://aviation.stackexchange.com/questions/47644/how-does-a-helicopter-hover

Very good observation - helicopters actually do want to flip over, in the hover. While hovering, the helicopter is in an unstable equilibrium and the pilot will have to make constant cyclic inputs to prevent the heli from flipping indeed.
Your observation of constant forward cyclic deflection is when flying forward, and this reveals the stabilising factor: airspeed.

The incoming frontal horizontal airflow component wants to blow the rotor backwards, which would actually happen with a centred cyclic. Maintaining forward cyclic prevents this from happening.
But the required forward cyclic input is very small, still requiring close attention from the pilot. In order to create an equilibrium state requiring a larger forward cyclic deflection, helicopters have stabilisers at the tail. With a nose-down tilted fuselage, forward velocity creates a nose-up moment.
The helicopter fuselage follows the tilt of the rotor plane, moving the CoG backwards, as depicted below. This creates a stabilising moment nose-up.

The two torques on your picture (lift+weight force pair and thrust+drag force pair) cancel out when the rotor is not tilted relative to the craft. The real reason is that forward speed increases lift on the advancing side, which creates the same effect as aft cyclic. And that effect isn't subtle. It also changes the behavior from slightly unstable at hover to slightly stable at high speed.

@JanHudec 1. rotor blowback, as mentioned in the first bullet point. And indeed, the mechanism of rotor blowback is as you describe, causing blade flapping. 2. Horizontal stabiliser. 3. The fuselage is tilted nose-down at forward velocity and the two torques do not cancel out, as mentioned in this answer

The first point would then deserve explaining. From the term “blowback” I don't understand the mechanism it is supposed to describe.

Bullet point 3 appears to be the pendulum/rocket fallacy. The aerodynamic force is still perpendicular to the rotor, thus in line with the CoG. There are videos on YouTube demonstrating that a tilted rotor stays tilted.


text:
how missiles or rockets change direction if gyroscopes prevent any direction change? they would bring back the rocket to same path?
Gyroscopes are instrument which prevent any wobbling or direction change but then how rockets and missiles change their directions. To change direction we have to give signals to gyro or to the servo(which control flaps) directly.

I think you are confusing gyroscopic stabilization with gyroscope instruments used for navigation.

Please explain your reasoning. Are you thinking that the rocket is a gyroscope?

The question is closed and can't be answered, but "Gyroscopes are instrument which prevent any wobbling or direction change" aside from the confusion between sensor and effector gyroscopes, reaction wheels / huge gyroscopes don't prevent turning, they just respond to torque with precession. Asking to reopen, as the question is very clear, it just includes two misconceptions that need to be explained.

For air-to-air missiles, check out https://en.wikipedia.org/wiki/Proportional_navigation The gyroscopes are generally in the missile seeker head, and sensors on them detect and measure the rate of change of the Line of Sight (LOS), and feed that to the flight control system to determine the collision course.

Gyroscopic rigidity in space means that a spinning gyroscope will stay aligned in the same direction while it is spinning. A rocket or missile is not a gyroscope.
Rockets and missiles may contain or use gyroscopic instruments as a method of navigation. That in no way means that the rocket or missile must stay aligned in the same direction as the gyroscope. The gyroscope is just a means to maintain a sense of direction.
For example, most aircraft have gyroscopic instruments. The pilot uses these to maintain awareness of Magnetic North even when experiencing compass errors. This in no way prevents nor assists the turning of the aircraft.

the gyroscope rotor in an attitude instrument is suspended by a gimbal assembly which allows the aircraft to pitch, yaw and roll without applying any torques to the spinning gyro, which swivels about freely as it "remembers" where the horizon is.
Those torques would cause the gyro to precess and thereby furnish wrong attitude information.
If the gyro rotor is rigidly coupled to the airframe, then as the airplane rolls, the gyro rotor rolls too and hence cannot tell you where the horizon is. As it does it will be producing a gyroscopic countertorque to the airframe, but for an attitude gyro this countertorque will be small.


text:
Model of aircraft banked turn
I'm trying to write a model of aircraft motion during a banked turn, so for say a 60Degree roll angle constant altitude turn will require 2g lift.  However to achieve this lift the aircraft has to pull incidence.  However would this produce a nose up inclination in addition to the 60Deg roll angle ?

Related. Note in English 'incidence' is not what you think, the proper word is angle of attack or pitch angle. In other languages that would be correct.

Welcome to aviation.SE! I'm not sure what you're asking, but if you want to know about how turns and angle of attack are related then this question or this one

@mins it's important to clarify that angle of attack and pitch angle are different angles (as I'm absolutely certain you're well aware). Your explanation could be read to mean those are the same, and that might set someone new to flight physics on the wrong track. Hope it's OK to note.

@CptReynolds, it's a good point, my wording was not very clear. I made a graphic earlier to compare basic angles involved in lift.


text:
Are supersonic passenger aircraft still realistic?
I was wondering if supersonic passenger aircraft like Concorde or the Tupolev Tu 144 can still be made and flown profitably. The Tu 144 failed because it was poorly designed. And Concord failed because of its high profile crash.
After these, what are chances of supersonic passenger aircraft coming back? One popular news I heard was of boom supersonic jet https://boomsupersonic.com.

The Concorde was on its way out well before the crash, it just helped speed along the inevitable.

Perhaps you should change "still" to "ever".  I think both the Concorde and Tupolev were much more about technical chauvinism than about practical economics.


text:
Reducing popularity of 4 engine aircraft
We can see that now most latest airplanes by Boeing and Airbus like 737 max or A350 have twin engine configuration instead of 4 engine. And many airlines are discarding iconic 747s and A380s. What is exactly reason for dying popularity of these iconic jets?

I definitely would not mention 737 MAX in this context. It is a hideous example of beating a dead horse. An exhumed  archaic design at best...

Cost and reliability.
At the dawn of the jet era, no jet engine was powerful enough to use just two. They also tended to fail a lot, so even once two was powerful enough, one still wasn’t, so quad-jets ruled the skies.
However, power improved quite rapidly, and it soon became practical to build large twin-jets, which were significantly cheaper to buy and to fly. But they were restricted to land routes because the engines still failed too often.
This led to the creation of tri-jets, which were conceptually just twin-jets with a spare engine in the tail; regulators deemed that safe enough for oceanic routes, and quad-jets mostly died out.
Then, eventually, the engines got powerful enough that twin-jets could fly several hours on one engine, and reliable enough that it rarely happened anyway, so regulators decided twin-jets could be used on oceanic routes, and tri-jets disappeared overnight.
The sole remaining case for quad-jets was aircraft so ridiculously large/heavy that they simply couldn’t fly on one engine, no matter how powerful. That is where the B747 and A380 fit in.
The B747 did well in that niche for decades. However, by the time the A380 was launched, the inherent problems with hub-and-spoke networks had become glaringly obvious, so the industry had started shifting to more point-to-point routes that were better served by smaller aircraft. After initial flurry of orders for the A380 (and remorse when buyers had problems filling them), the market dried up, and production ended for both aircraft.


text:
How can PreciseFlight speedbrakes double the drag while being so small?
Look at this photo of some PreciseFlight© speed brakes:

On the website it is claimed that these little red plates can double drag and descent rates. I cannot believe that. Can this be true, and if yes, can you explain please how these small things can double the drag ?

What about these speedbrakes, essentially big holes? Same manufacturer, same doubling of drag/descent rate.

@mins surely this isn't serious ?

@Programmer It is serious. And don’t call him/her Shirley.

Essentially, they are selling a spoiler.
The way they can claim "doubling the drag" may be as follows:
The device spoils lift, thereby reducing lift cofficient.  This results in the aircraft either having to fly faster to make the same lift, or at a higher AoA.  Analysis of airfoil drag polars do show a sharp reduction of Lift/Drag ratio as AoA increases.  Increasing speed will also increase drag exponentially.
The spoiler is not to be confused with flaps, which increase lift coefficient, allowing the aircraft to fly slower while maintaining lift (higher flap settings are generally used strictly to increase drag), making them useful for landing approaches.
While spoilers are valuable on extremely low rate of descent aircraft such as gliders, benefits of higher approach speeds are dubious for powered recreational aircraft.  Some pilots may favor them over the old fashioned, but highly effective, forward slip.

Oh yes, the reduction in lift seems plausible, thank you ! +1

Also note that the Mooney's equivalent flat plate area is only 400 sq in, so the speed brakes are easily most of the way there on projected surface area alone.

One can see how jet pilots might like them, adding drag rather than changing throttle.  Need to know their effect on the stall speed of the aircraft.

"The device spoils lift", if it spoiled lift it would be spoiler, not a speedbrake. If they stalled the wing on this small width, it would be a limited effect. I rather think the holes create large eddies, an efficient source of drag.

@mins this device came out more than 20 years ago.  Some pilots liked it because it helped stick fast landings.  My preference is a tail speedbrake, like the F-86 Sabre has.

You are on the right track but missing a key ingredient: The local loss of lift spoils the lift distribution over span, increasing induced drag substantially. I predict that the strongest effect of these spoilers is at low speed when induced drag is dominant, but did not look for proof.


text:
What does CPLD mean in aviation in general and on this altitude alerter?
I saw the shortcut CPLD on this altitude alerter from a Cessna 210, and could not work out what it could possibly mean:

What does it mean on this altitude alerter, and if CPLD is also used elsewhere in aviation, what does stand for there ?

The unit in the image is a Cessna AA-801A altitude alerter.

CPLD Green Lamp:

Lights when airplane reaches selected altitude and Integrated Flight Control System altitude hold mode is automatically engaged

CPLD would be short for coupled, indicating a system is linked to the autopilot.
You can see this and read more in this C210 POH, page 559 in the pdf (Supplement 47, page 4).

Ahh … Maybe I should read both the P210N and the T210N POH in the future - there seems to be a lot of information in the latter that isn't in the former. Thank you very much ! +1


text:
What is the metal sheet in front of the engine called on a Cessna 182 or similar?
I need to know the name of that metal sheet covering the front of the engine in small Cessnas (specifically the Cessna 182), just behind the propeller. I mean the one where the cowl plugs are put into:

Do you mean the cowl(ing)?

@ymb1 not broken, just some dust ! ;) I have added a picture - the area circled in red is the part I mean.

@StephenS maybe - I have added a picture.

@ymb1 I mean the first one, that one with the holes in it.

The forwardmost part of the cowling is called the Nose Bowl.  On most modern airplanes it's made of fiberglass, and attached to the adjacent aluminum of the main cowling with rivets designed for composite to aluminum joints.
On most planes the nose bowl is split in two along with the rest of the cowling, so the upper half is part of the top cowl and the lower half part of the lower cowl. A lot of older airplanes have one piece nose bowls that attach to the main cowl with screws, and you had to remove the propeller to remove the nose bowl itself.

Give me time to figure out the gag....

Your sense of humour is actually close to mine lol.


text:
How are two seats supposed to fit side by side into a 3 ft 8 in (~1.15 m) wide cabin?
According to GlobalAir, the Cessna P210N "Pressurized Centurion" has a cabin width of 3 ft 8 in (~1.15 m). However are two seats (plus some space inbetween to be able to get through to the rear seats) supposed to fit into that space ? These seats can't be more than 40 cm wide ! Even I would only just fit on them, and I am not very thick !

I suspect they simply made an error.  From the picture (and experience of similar Cessnas), I think it's probably closer to 5 ft 8 in, which suggests whoever typed up the web page misread the 5 as a 3.

@jamesqf I don't think that, because the three-view in the POH of the Cessna P210N suggests a similar cabin width.

The seat I'm on is 40cm wide and I fit just fine.

@Programmer: Suggest you take a measuring tape out to your local airport :-)

You don’t get into the back of Cessna’s by going between the seats. You pull the seat forward as far as it goes and get into the back directly. You do need to go between the seats to get to the third row, but only small people fit there and there’s enough room to squeeze through.

Some dimensions

(Source)
Notice that the cabin cross-section at seat location is closer to rectangular than circular.

(Source)
So the interior cabin width is 105 cm, 42" at seat location. That is 3' 6". I guess the seat squabs are around 18" wide.
According to Wikipedia concerning commercial airline seats:

Since the beginning of the 21st Century until 2018 average seat width decreased from 18.5 to 17 inches,

So it's similar to economy class on an airliner.

The Cessna 210 Centurion has a maximum cabin width of 3’8” or 44” or 112cm. It is actually one of the larger single engine Cessna piston powered aircraft. The very popular Cessna 172 only has a 3’4” or 40” or 102cm cabin width.
Yes, the seats are very narrow but I can’t find any exact measurements.

Can you also tell me where the cabin width is usually measured ? At the widest point, or on the floor ? This can make quite a difference when the fuselage is about cylinder formed !

@Programmer Widest point.


text:
How much drag is actually caused by open cowl flaps?
I am modelling the Cessna 210 for FlightGear, which has cowl flaps. I want the model to be as realistic as possible, and so, I want to know: how much drag do cowl flaps produce ? I could not find any data on this in the Internet.
Another airplane in FlightGear, the Cessna 182, has already cowl flaps modelled, and they cause an airspeed increase of about 20 kts. Is this normal ?

Turbo 210 driver here. Our closing our cowl flaps in cruise typically gains us 3-5kts.
Who ever claims 20kts for closing cowl flaps is insane. Must be confusing them with speed brakes

Yeah I’m not buying a 20 knot reduction from using cowl flaps, either.

Thank you very much ! Actually it wasn't anyone "claiming" that - I was talking about a model in FlightGear (a free flight simulator), and these (as we know now) unrealistic 20 kts were simply due to a lack of precise data. Thanks to you and the other answerer we have that now ! :)

I did some flight testing last night in a C182, and I saw a speed increase of 3-4 knots when I closed the cowl flaps at cruise. While I won’t pretend my methodology was rigorously scientific, the results were consistent enough across different flight profiles that I’m confident in saying FlightGear’s 20 knots is grossly incorrect.
The C210 cruises quite a bit faster than a C182, so even same-sized cowl flaps should cause more drag, but I’m not sure how significant the difference would be. Maybe 10 knots? Without a C210 to test, I can only guess.

Thank you ! At least the C182 will now have realistic drag increase :D


text:
Which external lights are present on a unmodified Cessna P210N?
What external lights are present on a unmodified Cessna P210N "Pressurized Centurion", and where are they placed ? I've looked through the POH and searched on Google for e.g. "cessna P210N external lights", or "lights", or …, but I could not find the information anywhere, and sadly I don't have an airfield nearby where I could look at a real one.

It varies from year to year or A/C to A/C depending on factory options, STCs, etc.  Typically the P210’s exterior lights consisted of:

Red/Green/White navigation lights in the wingtips and tail.
Red omnidirectional anticollision beacon on top of vertical fin.
L/R wingtip white strobe lights.
Underwing mounted courtesy lights.
Cowl mounted landing and taxi lights.

See this P210N POH, Section 6: Weight & Balance / Equipment List and Section 7: Airplane and Systems Description.


text:
What is meant with "ultraviolet instrument lights" in the POH of a Cessna 310B?
In the POH of the Cessna 310B, two "ultraviolet lights" mounted in the overhead panel and lighting the instrument panel are described. They have starter buttons, to turn them back off the dimming rheostat has to be momentarily set to zero intensity. But it is left unclear what kind of lights they are exactly - are they real UV lamps, or just normal filament / LED lamps producing blue-violet light through the blue-colored lenses ? If they are real UV lamps, wouldn't you risk getting burned from the UV rays ?

I suspect they were low powered black light (UV) lights under the glareshield (?) which are pointed directly at the cockpit instruments, whose faces, numbers, needles, pointers, etc. were coated in a phosphorescent, shining brightly when illuminated by UV light. Exactly why Cessna made such a choice back then, is unknown. One possibility is that it produces smooth, uniform, illumination of critical flight instruments at night, without additional visible light, which degrades night vision.

They are mounted in the overhead panel, on the ceiling of the cabin.

@CarloFelicione I guess that phosphorescent has a simple white color, right ?

Posted as a comment not an answer because I don't have any documentation, but UV lights are also known as "Blacklights", and are used to make fluorescent materials glow. I suspect that there is fluorescent paint on the gauges, and the UV light just makes them stand out more at night. (Also, no, you're not in danger of "being burned by UV rays". Shortwave UV-C is dangerous, but the longwave UV-A produced by commercial blacklights is completely harmless at normal intensity.)

Ahh, I have looked up the part number from the IPC for the UV lamp, and wbparts.com indeed classifies the emitted light as Ultraviolet light. So this makes sense ! Thanks for your comments.

I would love to see a photograph of the panel lighted that way.

@ricardomenzer Sure thing: https://ibb.co/188gXZd

I meant the real thing @TheEagle

@ricardomenzer I know, just had to do a late April Fool's Joke ! ;)

The UV lights were used because they made the white instrument and panel markings glow brightly without affecting your night vision. It was one workaround alternative, after radium paint was abandoned, to get a similar effect of lighting only the letters and markings. Nowadays the same effect is achieved with instrument post lights and internal backlighting of control panels shining through letters.
The lamps would be UV-A lamps, typical "blacklight" bulbs, and back in those days would be gas filled low pressure mercury vapour lamps, like fluorescent bulbs.
Like fluorescents, they require a ballast (a capacitor) to provide an electrical jolt to start them up, which is what the starter button is for.
If you have them shining at the instrument panel, you aren't going to get that much UV exposure, but probably after many hours if you had some of the UV shining on your forearms and hands, you might start to get a sunburn. It would depend on what sort of hood or shield is over the light to control where the light shines.
The issues of extended exposure to UV, and no doubt reliability issues with mercury vapour lamps and the fact they don't provide useful illumination beyond making white things glow, is probably why they faded from use over the years.

"The issues of extended exposure to UV, and no doubt reliability issues with mercury vapour lamps and the fact they don't provide useful illumination beyond making white things glow, is probably why they faded from use over the years." - Also, mercury, which probably won't be good for the pilot if the lamp breaks in a crash.


text:
Why is this Cessna flap position indicator marked so irregularly?
Look at this flap position indicator as found on Cessna 310 models:

(source: eBay)
I would have expected it to be marked at 5° intervals, but it is marked irregularly instead (apart from the "big" marks at 15° intervals). Does anyone know why ? I mean, when the intermediate marks are placed irregularly as on this gauge, they hinder reading an accurate value rather than helping it ...

Whatever the mark "definitions" are, the marks appear to be 5 degree increments so why is the spacing not even? I think that's what is being asked.

@radarbob exactly

Because it was the analog world and no other (easy) solutions exist. Providing an exhaustive answer will require too much space here, but I'll give the idea with the help of some figures.
So, this is the back of that instrument:

as you can see, there are three contacts. How do they work? Let's check the electronic schematic:

This is a Desynn system. The trasmitter needle rotates over a resistance and changes the amount of current delivered to the receiver (indicator) that rotates depending on the magnetic interactions generated by the three star-connected windings (you can find a good explaination in this video).
And then, let's look at the actual "sensor" (not the best picture):

The round box on the left is the tramsitter, while the bolt on the right is the one attached to the flap surface. As you can see, there are at least two joints between the flap and the trasmitter, and the movement of the trasmitter is no more linear with the angle of the flaps. This explains why the arrow doesn't move linearly, because not even the "sensor" (tramitter) receives a linear input.
The reason of having joints is probably due to space or other mechanical contraints inside the wing. The reason why not to fix this in the electronics is just cost and complexity of doing this in analog electronics of '50s.


text:
How do GA aircraft flaps stay in place?
On most small GA aircraft such as the well-known Cessna 172P "Skyhawk", the flaps are electrically actuated. Now - how do they stay at the setting selected by the pilot after extension ? Is there a bolt that is put into the flaps after the motor drove it to the selected position, and which is retracted again when a different flaps position is selected ?
They surely aren't hold in place by the electric motor, because that would mean that the flaps would immediately be pushed back into the retracted position by air pressure in case of an electrical failure.

The total flap movement during extension is relatively small. This means there will be a significant gearing-down of the electric motor rotations between the motor shaft and the flap actuation axis. If this is accomplished with a worm gear drive it is possible to design the worm advance angle in such a manner that the friction normally present in the system will cause the gear drive to lock if it is being forced backwards. This allows the use of a relatively small electric motor to actuate the flaps and to make it impossible for the aerodynamic forces on the flap to spin the motor backwards through the worm drive and cause it to lose position.

Specifically worm drives generally by definition cannot be drive by the load https://en.wikipedia.org/wiki/Worm_drive#Direction_of_transmission

@GremlinWranger your link which contained an image of such a worm drive which made me immediately understand ! ;)


text:
Does the radial needle of a HSI automatically deflect to the correct position when tuning the NAV radio to a localizer / ILS?
At least on small aircraft, the HSI is slaved to the NAV1 radio. The NAV1 radial is selected with a small knob of the HSI. Now, when I want to fly an ILS approach I don't need to set a radial myself as an ILS / LOC has only one. But if the runway has a different orientation than the radial / CDI needle o the HSI, this is confusing. Do I need to set the correct radial myself, or does the NAV radio / autopilot do that automatically ?

Yes, you need to set the correct course yourself.
There is no servo motor inside a mechanical HSI that can receive a command from an autopilot to change the course for you, it is designed to be manually set by the pilot.
In my experience in GA with KAP140 autopilots, these are very basic non-integrated "add-ons" that need a lot of careful monitoring as they blindly follow the course needle (whether you set it up correctly or not).
These basic autopilots are not sending any data TO any flight instruments (including the HSI).
As you know, when you engage NAV hold the autopilot simply turns the airplane to intercept and center the needle. It's pretty limited in its capabilities.

It depends on your instrument suite.
If you have just a radio with connected HSI, you have to set the course yourself, because on the radio you only set the frequency and there are hundreds ILS installations with the same frequency across the world.
If you have flight management system with a waypoint database where you set the ILS by its identifier, it will set the course for you. Airliners had that for some time, but integrated avionics suites are making their way to small airplanes as well that have it (together with full RNAV capability where you just select waypoints and the HSI gets slaved to the GPS).

I'm referring to small GA aircraft with steam panel. I understand that the course cannot be set just based on the freq - but the autopilot (for example the Cessna 400 Nav'O'Matic) does find the correct radial - so why couldn't it set the radial on the HSI too ?

@Programmer, the autopilot does not really know the radial at all, it just steers until the needle stops moving.

Depends on the autopilot, some autopilots require a course to be entered in the FMS before they can capture the localizer. General Aviation autopilot usually don't suffer from such weaknesses.

@JanHudec ah, I didn't know that ! So I guess if you engage the autopilot while flying away from the radial you will have to go around the earth once to capture it, right ?

@Programmer, no. The autopilot simply turns left when the needle is on the right, moves to the right, or accelerates to the right, and vice versa. If you are on the right, but facing away, turning left will get you further from the radial until you either make 180° or the autopilot disconnects because the maximum deflection is exceeded (you could capture a side lobe outbound otherwise). I think some autopilots will reverse the sensing when the dialed course is more than 90° off your heading, so they'll capture the outbound radial instead.

@757toga I understood “HSI” to simply be generic name of the instrument, so I assumed it might include glass ones, including if the instrument is just drawn on the ND. I agree a mechanical one won't be able to connect to FMS at all.

@Programmer Your autopilot doesn't "find the correct radial" when you tune in a localizer because a localizer transmits only one course (unlike a VOR which has 360).
There is no course that needs to be found because there is only one course.


text:
What does Airspace 24 mean in this chart supplement?
I found this line in Leesburg Executive Airport (KJYO)'s chart supplement:

I have looked in the Chart Supplement Legend under section 29 and there is no information about such an airspace. At the bottom of the legend it says to look at AIM's Chapter 3 for more details, but none can be found there. I googled this to no avail.
I am guessing that whatever it is might have something to do with KJYO's situation. It is located in the DC SFRA and has an FDC NOTAM "Leesburg Maneuvering Area" which lists required procedures when operating in and out of the airport. Don't know how "24" comes from all that, though.

Looks to me like something that should be submitted through the established channels as a mistake or in need of clarification--

It’s a special case related to the DC SFRA. NOTAM for this airport !JYO 01/008 JYO AIRSPACE SEE FDC 1/1155, 9/1811, 0/0053, 9/1812, 0/3929 ZDC SPECIAL SECURITY INSTRUCTIONS 2001150003-PERM

It looks like a mistake of some kind. The next release of the Chart Supplement is valid from 2021-04-22 and the airspace line has been removed completely from the KJYO entry.


text:
How are bags transported from the terminal to the airplane?
I'm curious how bags are transported from the terminal sortation system to the aircraft. I'm mostly trying to understand the "average tarmac distance" a bag will travel. If anyone has direct insight into that metric that might be even more helpful than understanding the process.
I grabbed a screenshot of the United Terminal at DIA to try to map out how this could be implemented. Can anyone help with insight into which process implementation is generally used in the industry?

Each gate has a "sort point" and bags are transported a short distance from that gate sort point to the plane parked at the gate.

One sort point serves "N" number of gates. One baggage handling Cart serves only one plane. (How big is "N" if this method is used?)

One sort point serves "N" number of gates. One baggage handling Cart may serve several planes, detaching a section of the the train at each craft.

Are any of these methods used? Or perhaps could several sort points feed one aircraft? Does this vary airport-to-airport or airline-to-airline? Who is generally responsible for the design of the process - the airport or the airline? Do ULDs have a different process than each-loaded bags? What about smaller regional jets loaded at the far ends of the terminals - are their sort points further away? How does the process look for offloading bags from the aircraft?

I don't think there is a universal answer to this question, each airport may have different baggage handling systems/procedures.

I agree with Ron.  Procedures will vary widely and depend on airport layout, as well as equipment and personnel available throughout the day.  For example, a modern busy airport with underground conveyors and automated sorting would benefit from the apparent efficiency shown in the first photo, while a small regional airport with one licensed tug driver would necessarily need to follow the example in the third photo.  This might be a useful and interesting topic if you could distill the question into one more answerable or help us understand a specific problem you are trying to solve.

And what is a ULD?

@MichaelHall ULD = Unit Load Device. i.e. container into which freight is loaded, then the ULD is loaded on the plane.


text:
How are panel codes like xfoil able to model turbulence and predict drag?
Since Xfoil is using potential flow theory, how is it able to predict boundary layer and separation?  If I'm adding perturbation terms aren't those still made with fundamental flows?

The answer is in the resolution of the boundary layer by solving integral equation, for which a potential solution is needed (see this answer). XFoil uses Thwaites method coupled with Michel method. In particular it uses the local Reynolds number to understand if transition happened or if separation happened on the airfoil surface.

XFOIL uses a potential code for inviscid calculation (the prompt then reads OPERi) and outside of the boundary layer in viscous mode (OPERv).
The boundary layer calculation needs the speed and pressure information from the potential part but then uses an integration method for the boundary layer and iterates the solution, until a set of residual errors is driven below a pre-determined threshold. This iteration is needed to find the correct boundary layer thickness that agrees with the parameters of the potential flow solution around the airfoil plus this boundary layer.
The boundary layer formulation used by XFOIL is described in:
Drela, M. and Giles, M.B.
Viscous-Inviscid Analysis of Transonic and Low Reynolds Number Airfoils AIAA Journal, 25(10), pp.1347-1355, October 1987.


text:
How can I make a serious wind tunnel?
I am looking for specifics of building and the operation of low speed wind tunnels, but most diy wind tunnels on internet are improved versions of science fair projects at best.
What would I need to keep in mind if I decide to make one myself? Image for size reference.

Start with roundly a million dollars...

How many square feet of floor space?  How low a Reynolds number?  What budget for maintenance?  For how many years?

@CamilleGoudeseune 60ft*40ft space, low reynolds number from 200k to 1 million or more, 65k-100k usd budget... mostly aimed at mid size UAV testing of upto 5 metre wingspans and some other research

You want to put a complete 5 meter UAV inside this, or test on scale models?

@ZeissIkon scale models

The fans and electronics are going to cost more than that. What are you trying to measure?

I would like drag, lift and moment polars, oil flow visualisation patterns, aeroelastic effects on half wings. and set incidences and trim properly

@RonBeyer I can cnc some wooden fans, I have a good composite manufacturing experience as well, So maybe I can make large composite blades

For a project you'll spend $65,000+ on, working from plans that didn't come from a professional with experience designing wind tunnels seems like an opportunity for an expensive mistake or lessons learned. At some point, "you get what you pay for".

While fans aren't difficult (but can be expensive), the hard part here is straightening the airflow. That takes far more space than your smallish test chamber. This is well evidenced by NASA's wind tunnel at Langley (https://www.nasa.gov/vision/earth/improvingflight/16ft.html)

It may be possible to find public-domain plans,

This question sets forth a project of considerable undertaking.  Nevertheless, a relatively small wind tunnel is feasible, particularly for low-speed work (i.e. low Reynolds number), if there is willingness to use care and understand the technical issues in smoothing airflow and eliminating turbulence in the free stream flowing through the model test section (about 1/16th the area or even smaller, compared to the test section pictured in the question).  This link here will show the similarities between a large engineering wind tunnel, and a much smaller version used at the same facility.  The smaller version has been ideal for low-speed work, and has been used advantageously in that realm.  A description of the main facility for the associated large, engineering wind tunnel is found here.  In the United States, much work has been done with intermediate sized wind tunnels capable of reproducing results of equivalent quality to those obtained in the large wind tunnel mentioned herein.  These wind tunnels are located at a) Princeton University, b) University of Illinois Urbana Campus, and c) Notre Dame University.  These wind tunnels, although relatively small, are quite substantial. The wind tunnel used at the University of Illinois Urbana has produced engineering results of the highest quality in the study of airfoils, and in comparison of those results with computational methods available from various sources.

It depends on the cross-section and speed of airflow. The tunnel itself is just a duct. Is the power usage for fan that makes it expensive

You also require a means of smoothing out all the velocity gradients and eddies in the flow before it enters your test section. This is done my filtering the incoming air through a series of 10 or so screens with the fineness of a window screen, completely spanning the inlet cross-section, and set about 4 inches apart.


text:
What if I lost electricity in the night when my destination airport light need to activate by radio?
This is an interesting question I've discussed with my friends
As the title says. In this case your transponder doesn't work. Despite the tower can use light to guide you. But:

It's totally dark and you're invisible
The tower may be at off time

What can we do?

It happened on February 5, 2017 near Paris Airfield, Texas; here's one account of the incident. ATC managed to find the pilot's cell phone number and text him, after which they managed to manually turn the lights on at another airport and direct him there.

@user70523 -- maybe you are on to something-- why do we no longer carry parachute flares to light the ground below for emergency night landings, like airmail pilots used to to in the 1920's when flying the night mail in their DH4's?  (This is well described in Lindbergh's book "The Spirit of St Louis" -- along with accounts of bailing out when the flare showed no landable terrain below... )

Use your handheld radio, or go to another airport that's lighted, or call or text someone on your cell phone, or keep flying till (full) moonrise or dawn, or fly to the handy nearby desert dry lakebed where space is unlimited and the white surface will visible to dark-adapted eyes even by starlight.  In the latter case, to compensate for lack of depth perception, you may need to use the procedure used by floatplanes landing on glassy water-- maintain a constant, low descent rate till the wheels touch.
Or do a low-altitude buzz job on a nearby neighborhood, all-night gas station, etc-- maybe you'll get someone's attention.  (But try buzzing the airport first-- if anyone's there, they should soon realize what is going on.)
Apparently flying in triangles used to be a distress signal to ATC, but has now been abandoned  (link to "Quora" answer).

This actually happened to me once, our destination was an uncontrolled airport with pilot-controlled lighting.
Luckily everything didn't die at once. The first clue was the GPS screen going blank. After some investigation, I found that the generator had failed and the battery was going dead. I quickly turned off everything electrical, including all the lights inside and outside, and used a flashlight to see the instruments.
Once we were close to the airport, I turned on one nav/com radio (not the GPS/nav/com) and clicked on the airport lights. I left all the lights off and made radio calls including our lack of lights with the remainder of the battery power. It worked out fine, nobody else was around.


text:
Does temporary paper student pilot certificate expire?
I didn't receive my plastic student pilot certificate.
Can I use my temporary paper student pilot certificate to take checkride in the USA? Does it expire?

The temp certificate only for solo.
The temporary student pilot certificate remains valid for a duration of 120 days from the issuance date. Solo flights are restricted to a designated geographic region, and the student pilot is prohibited from transporting passengers or cargo. It is mandatory for the student pilot to have both their temporary student pilot certificate and government-issued photo identification in their possession when flying solo.
https://www.ecfr.gov/current/title-14/chapter-I/subchapter-D/part-61/subpart-A/section-61.17

Good answer.  I would suggest posting a quote from the link so the answer from 61.17 is capable of standing on it's own.


text:
How to avoid conflict in VR military training route?
I'm new pilot. I know there is 1 mile distance from cloud above 10000 ft. Because plane can fly as fast as they want.
However I noticed that like VR1203, they're military training route where more than 250 knots are permited below 1500 ft under VFR. So how do we avoid conflict? What is my flight plan need to fly across such route?

VR routes have an upper altitude limit that is easily reachable by GA aircraft.  Look up what that is and just fly over the top of it.  (1500ish?)


text:
What approach method does tower possible to give me?
I'm a student pilot. ATC is a difficult part for me.
So far when I fly cross-country, the only VFR approach I hear from ATC is "straight to runway XX". Is there any other approach the ATC will instruct me? What are they?

This is an excellent question to ask your instructor. They can sit down with you and discuss the various possible pattern entries: what you can expect ATC to say and what you would do with the airplane in response. And you can ask to fly with your instructor to towered airports and practice different entries.
What country are you flying in? In the usa, the AIM 4–3–2 provides a general overview of operations at towered airports—that entire section would be a good read. ATC follows a different document, JO 7110.65; pilots are not required to be intimately familiar with the 7110.65 (just as ATC is not required to be intimately familiar with the AIM) but if you know where to look you can gain some good insight and learn what phraseology you can expect to hear on the radio. The .65 3–10–1 lists phraseology to be used when specifying pattern information (and see also 3–8–1):

PHRASEOLOGY-
ENTER LEFT/RIGHT BASE.
STRAIGHT-IN.
MAKE STRAIGHT-IN.
STRAIGHT-IN APPROVED.
RIGHT TRAFFIC.
MAKE RIGHT TRAFFIC.
RIGHT TRAFFIC APPROVED.
CONTINUE.
NOTE-
Additional information should normally be issued with instructions to continue. Example:
"continue, report one mile final"; "continue, expect landing clearance two mile final"; etc.

The Pilot/Controller Glossary is also a very good source of information; for example the entry for TRAFFIC PATTERN includes these helpful notes:

ATC may instruct a pilot to report a "2−mile left base" to Runway 22. This instruction means that the pilot is expected to maneuver their aircraft into a left base leg that will intercept a straight−in final 2 miles from the approach end of Runway 22 and advise ATC.
ATC may instruct a pilot to report "5−mile final" to Runway 22. This instruction means that the pilot should maneuver their aircraft onto a straight−in final and advise ATC when they are five miles from the approach end of Runway 22.

Note that in the absence of a specific pattern entry instruction, the default expectation (just as at a non-towered airport) is that you will enter the pattern by way of the downwind. However, you should be very certain to ask if they intend you to cross over the airport in order to enter the "correct" downwind; it is always better to ask for clarification than to make assumptions. In my experience it is more often intended that you will enter the closest downwind, even if that is not the "correct" downwind per the Chart Supplement.

It's so good to know where to find what ATC could possibly say.
I know I can discuss with CFI but it' hard to discuss with CFI for all circumstances. Thank you very much for the references

The key here is to get the ATIS information early, and to understand your position in relation to the runway in use.
ATIS information will usually say which runway is in use.  Knowing that and knowing where you are in relation can help you anticipate what the tower's instructions will likely be.
One of the busy towered airports I fly into as a GA VFR pilot often gives me instructions to either enter right downwind for runway 34R, enter right base for 34R or report the shoreline for a straight in 16L.  All based on where I'm at in relation to the field and how busy the pattern is.


text:
Why does Garmin Pilot tell me a wrong magnetic variation?
For example. In KCNO, the mag variation on sectional chart is 11.5E. But on some websites and in Garmin pilot, it says it's 14E. Why would this happen?

Typically, the data is taken from the respective national aviation authority.  The FAA has incorrect information for KCNO in its database.
https://www.faa.gov/air_traffic/flight_info/aeronav/aero_data/NASR_Subscription/

Click on the current 28 Day NASR subscription.

Download the Airports and other Landing Facities zp file

Open the APT_BASE.csv file

CNO shows a magnetic variation of 14E reported in 1980.

How can this be reported to the FAA?

https://www.faa.gov/air_traffic/flight_info/aeronav/aero_data/


text:
Where can I save the cost of private pilot training
I'm a Chinese who want to take private pilot training.
I know there are some personal factors that can reduce the expenses. But Is there any other factors like posistion of the flight school which can save cost? Are some states are generally cheaper than other states?

What country do you intend on training in, that will vary this answer greatly.

I prefer the USA of private pilot

What do you mean by 'personal factors'? Are you only interested in location?

One factor is the cost of 100LL fuel, and generally you will find the lowest price for that in Texas and states immediately around it.
Other factor is to choose to do your training in the smallest trainer you can fit into, like a Cessna 15x.
You might also want to consider doing your training somewhere other than in the US. When you get the foreign PPL you can then take the test for the US PPL and apply to convert your license to a US PPL.


text:
What is Automatic Radial Centering on a VOR indicator?
As the title says - some steam VOR indicators got an ARC indicator lamp. According to the POH of an aircraft featuring such a VOR indicator this means Automatic Radial Centering. What is that ? I couldn't find an explanation anywhere.

As the name indicates, this automatically centers the CDI needle, by selecting the appropriate TO radial. From the manufacturer of INS 422, an integrated navigation system including a VOR:

Pushing the remote automatic radial centering button enables circuitry to automatically position the digital CDI indication to provide a one-time radial "TO" the VOR station. The digital indications displayed on the CDI will then return to conventional operation, permitting the radial to be flown in a conventional manner.

Without this system to determine on which radial the aircraft is flying, the pilot must turn the OBS until the instrument indicates TO and the needle is centered. With the ARC feature, this is done automatically.


text:
How to calculate drag of a flat rectangular surface at given area, air density, airspeed and angle of attack?
I'm a complete noob in aerodynamics, and I'm trying to calculate the drag of a rectangular flat area, given the air pressure / density, area, angle of attack and airspeed. I've read this question, but it is about calculating the drag for two rectangular areas, whereas I need it for one area, and I couldn't derive a formula for one area. Can you please help me with this ?
I need this to get the drag of cowl flaps extended at an angle between 0 and 20 degrees for a FlightGear model.

You’ve got a lot more to consider than just flat plate drag in determining the overall change in drag due to opening cowl flaps. The whole airflow through the engine compartment changes. And because the cowl flap is not just a flat plate in the free stream but has some sides and is attached to the fuselage and has air flow from the engine compartment moving over the upper surface the flat plate drag equations are just a small part of it.

There's quite a variety of cowl flaps, which aeroplane are you modelling?

@Koyovis Cessna 182 S/T and Cessna P210N

Simply using the generic drag equation will get you within the ballpark required for FlightGear.
$$D = C_D \cdot \frac{1}{2} \rho V^2 \cdot A$$ with $C_D$ the flat plate drag coefficient and A being a reference area of your cowl flaps. The data for the correct Reynolds number is best used, with $$Re = \frac{\rho V \bar{c}}{\mu}$$ with $\bar{c}$ = mean aerodynamic chord and $\mu$ = kinematic viscosity of air. The Re uses the wing geometry to determine if the flow is laminar or turbulent, which has a large influence on the drag calculation.
So calculating additional drag for air density $\rho$ of 1.1 kg/m$^3$ (function of altitude) and airspeed of 150 m/s, we would get: $D = C_D \cdot ½ \cdot 1.1 \cdot 150^2 \cdot A = 12,375 \cdot C_D \cdot A [N] $. Now the only thing we need to do is look up the $C_D$ and determine reference area A in [$m^2$], and this is where things get a bit more challenging.
Note that we're calculating additional drag. When the flap is fully retracted and aligned with the cowling, additional drag is zero. Pull the flap open and extra drag is created - it will be less than bluff body drag, since the cowl flap opens to expel exhaust gases which prevents some of the pressure drag from occurring.
image source
To keep things simple, we can use bluff body aerodynamics with the front projected area as our reference A. For instance an airfoil $C_D$ of 0.045, with projected area of 0.002 * sin$\alpha$ [m$^2$]. $\alpha$ is the deflection angle of the flap.
The exhaust gas expelled behind the cowling flap prevents much of the pressure drag from happening, like in an airfoil where the flow gently foils back into the afterbody. Without the exhaust gas the $C_D$ would be higher, more that of a bullet. How much more depends on a whole lot of exhaust gas pressure parameters. Values of between 0.05 and 0.3 seem could be taken.

Oh, looks like you're not familiar with piston engine aircraft ! ;) Cowl flaps are not situated on the wing, but rather they are used to open / close a small hole in the engine cowling. In high performance situations such as takeoff or enroute climb they are opened to increase the airflow going through the gnine cowling and past the engine to have better cooling. In cruise and descent they are closed to reduce drag.

Have edited to use the more streamlined shapes of airfoil and bullet.


text:
Did any Cessna Centurion ever have floats or amphibious floats?
Most of the Cessna aircraft are also available with floats / amphibious gear. But I could find no information of a Cessna Centurion with floats or amphibious gear. Is the Centurion really not water-landing capable ?

Found one, but in all seriousness, the 210 in a retractable gear aircraft, the fuselage where the hard point mounts would be is probably not strong enough. Not sure about the fixed, but people say the wing is wrong?

@RonBeyer I can't see any floats on that - I mean such floats as in the other pictures below the big one.

@Programmer Ron was sarcastic, as suggested by "but in all seriousness"

@DeepSpace ah, now I see …

A check of the major float manufacturer websites, PK, Wipline, and Edo (now owned by Kenmore Air Harbor) suggests that nobody ever produced a float kit and STC for the 210, so the answer is no (I'm an ex bush pilot, around airplanes since the mid 70s, and I've never heard of one).
And this makes sense because the 210 was not really optimized for float operations, mostly because its minimum flying speed is too high, with a 67 mph published stall, thanks to a fairly unforgiving highly loaded NACA 64 series laminar airfoil in the cantilever wing introduced in '67 (a scaled down version of which was used on the 68/69 Cardinal), means a take-off and landing speed in the 70s, much too fast for seaplane operations in that weight/size range (ideally, you want to be able to take off well below 60 mph to have adequate hot/heavy/glassy water performance).
For more or less the same reason, the Centurion's little sister, the Cardinal, was also never modified for floats.  The lack of lift struts on either of those models is inconvenient for float operations, but aren't technical deal breakers (bracing the Cardinal's forward cabin structure would have been quite a challenge though).
No technical reason it can't be done, even on the RG version (you're removing the gear all the same whether it's fixed or folds, and there are lots of twins like Aztecs and Beech 18s operating on floats), but no one seems to have gone to the trouble to certify a float kit for it.
Add in the fact that the airplane's 180/182/206 relatives are far more suitable, it pretty much eliminates any incentive to develop a kit for the 210.

Let's imagine you manufacture floats for Cessna aircraft. The obvious candidates for float conversion would be those Cessnas with large engines, fixed gear and stretched fuselages. Big engines let you haul at max gross and furnish improved hot & high performance. Stretched fuses let you carry odd-shaped cargo. Fixed gear yields convenient attachment points for the float struts. Since you need a certain number of retrofits to justify your design investment, you'll choose the Cessna model that meets those criteria AND which was manufactured in the greatest numbers.
What all this adds up to is you'll pick a 250 HP Cessna with 6 seats and fixed gear and ignore anything that was built out in relatively small numbers. And: you'll ignore retractables because their use model doesn't match your target market.


text:
What does the small needle + scale on this turboprop's N1 gauges indicate?
Look at these weird turboprop N1 gauges:

I'm referring to the smaller needle at the top of each PERCENT RPM labelled N1 gauge. What does it display ? I have no idea.

I don't know anything about that specific aircraft, but just from what I know of gauges in general, it looks like the units digit. So the left hand one is reading 1% and the right hand one is 0%.

@GregHewgill ahh, yeah, if you look very close the left big needle is indeed deflected from the 0 mark a very little bit. Thank you very much, this was the pointer I needed ! :)

It duplicates the percent graduations in the large dial but at a finer resolution, with one percent increments.  It's just to make the individual percent graduations easier to discern at a glance without having to squint down at the gauge to judge where the needle's point is relative to the little hash marks, which are in 2 percent increments.
When the big dial moves from 0 to 10%, the small dial makes one full rotation. So when the big dial needle is at 5, or 15, or 25 etc, the small dial will also be at 5 (6 O'clock).
You can watch it in action here at about 1:25.

If the engine is at 95% RPM, the large needle will point halfway between the "90" and the "100" indication on the outer scale, and the needle on the small dial will point to the "5" mark on that dial.
The smaller dial makes it easier to read an exact RPM, to a precision of about +/- half a percent.

The smaller dial also makes it easier to judge if the RPM is changing and in which direction.


text:
Multiple COMM types on the same frequency?
In the manual for the Garmin GNC 255 on page 13, it is stated that:

When connected to a position source, the nearest station identifier will be
shown for the selected frequency. Frequencies with multiple types will have
an asterisk next to the identifier.

What does that mean ? Is there any airport that has their, say, TWR and APP on the same frequency ? If so, how does the aircraft's radio distinguish them ?

Is there any airport that has their, say, TWR and APP on the same frequency ?

Sure, there are plenty.  One I can think of right away is Kenosha Regional (KENW)

At Kenosha (while the tower is staffed), the person working ground control also provides clearances to aircraft on the same frequency.

If so, how does the aircraft's radio distinguish them ?

It doesn't need to.  You're talking to the same person on the same frequency, you're just calling them by a different name because you want to accomplish a different task.  All the radio knows is that you want to transmit on 121.875. What you say during the call is between you and the controller.

But then why does the GNC 255 display that there are different types for a freq and even  lets me select a type according to the manual ?


text:
What conditions must be met for Straight in Approach minimums to be published?
Looking at KSEE LOC-D approach, the final course is pretty much lined up with the runway. The MDA leaves you about 1200 AGL.
I'm thinking only circling minimums are published because it would be a very steep descent, but what is the criterion for this?

Does this answer your question? Why and how would I land straight-in from a circle-to-land approach? (the question is different, but I think the answers given cover yours too).

Yes that section in the AIM was what I was looking for. It just says when "the normal rate of descent or the runway alignment factor of 30 deg. (15 deg for GPS IAPs) is exceeded"


text:
Why do some GPS receivers suppress RAIM integrity warnings after you pass the FAF?
RAIM performs an integrity check 2NM from the FAF. If RAIM is lost before the FAF, one should execute the missed approach.
However, if RAIM is lost after passing the FAF, some GPS receivers will suppress the "RAIM Loss" message for 5 minutes to allow you to complete the approach.
Why does it allow you to continue the approach without GPS integrity for 5 minutes? Seems a lil sketchy to me

What receivers are you referring to that do this?  The specific hardware may affect why it's able to do this. (For instance, if there was an associated INS, that might affect things significantly.)

Welcome to aviation.SE! Could you add a link to a GPS manual or another source that mentions this behavior? It would probably help to get a better answer.

As ymb1 commented, RAIM was introduced in TSO-C129 receivers. These were the first GPS receivers certified and they were only approved for supplemental navigation (You were required to also have an approved nav system such as VOR as primary.)
RAIM algorithms are still present in the more modern SBAS capable receivers but are pretty much moot as long as the SBAS signal is present. SBAS provides an integrity signal that is more accurate and quicker to alarm than the RAIM algorithm.
It is also important to note that the TSO-C129 receivers were only capable of non-precision approaches (NPA). NPAs typically have an minimum descent altitude that provides approximately 500 feet ground clearance. Those limits keep you safe while using less accurate navigation systems (see also VOR and NDB.)
To address the question; when designing a system with an alerting function you have to deal with the possibility of false alerts and badly timed alerts. RAIM algorithms are not simple yes/no computations, so there's some gray area about when to alert. And losing RAIM doesn't mean you've lost acceptable accuracy. The FAA wants it to be safe but they don't want alerts that cause unnecessary go-arounds which introduce more risk and can create ATC conflicts.
Essentially there is a question of 'At what point in an approach would it be safe to continue if we lose RAIM?' You definitely wouldn't want to force a go-around 10 seconds from the missed approach point (MAP) due to loss of RAIM. For an NPA, it was determined that it was safe once you were past the FAF.
If you have reliably passed the FAF on the final approach course, you're 3-5 minutes from the MAP and there are no course changes. If you're good at the FAF, you only have to concern yourself with a potential fault that occurs between the time you pass the FAF and you reach the MAP where you either go missed or continue to landing.
The system safety assessment (SSA) addresses potential failures, their effects, and their probabilities. These are categorized by the hazards they create and whether they are detectable. The faults of concern are those that create undetected hazardously misleading information (HMI). For a NPA, the probability of undetected HMI must be less than 1E10-7 for the approach. Since approach period is 0.1 hr (6 min), the system must have an undetected HMI rate of 1E10-6/hr. (These are the same standards applied to VOR and NDB approaches.) The TSO requirements are designed to meet these safety requirements.
In the rare case of minimal satellites in view, no RAIM, and a sudden navigation fault there could be a significant change in position (and guidance) that would be detectable. With the narrowed CDI sensitivity past the FAF, any sudden position shifts that were great enough to be a hazard would generate a full-scale deflection which would trigger a go-around.


text:
How many Krueger flaps does the 737-700 have?
How many Krueger flaps does the 737-700 have? It has inboard krueger flaps, but I'm trying to make out if it has one or two.

It has 4 Krueger flaps (2 on each wing) and 8 slats (4 on each wing):

LE devices consist of four flaps and eight slats: two flaps inboard and four slats
outboard of each engine.

(Boeing 737 NG FCOMv2 9.20.20 - Flight Controls - System Description - Flaps and Slats)
You can see the Krueger flaps in the following image (thanks to ymb1 for the link):

(cropped from Wikimedia Commons, CC BY-SA 2.0)


text:
Is thickness-to-chord ratio constant along the span of horizontal and vertical stabilizers?
Their airfoils are usually symmetrical, I'm wondering if t/c (thickness-to-chord ratio) is constant along the span, unlike wings where it is not constant.

Is thickness-to-chord ratio constant along the span of horizontal and vertical stabilizers?

Generally, yes. The design of horizontal/vertical stabilisers is driven by maintaining control and stability in all circumstances, while main wing design has a major influence on operating costs (drag and weight).
For the main wings, the bending moment at the root is considerable. For aerodynamic reasons it makes sense to increase the aspect ratio as much as possible, creating a larger span for a given wing area. Increasing the wing thickness at the wing root creates a larger moment arm for counteracting the bending moment, allowing for lighter construction. Outside the wing root area, other considerations for flap/slat/aileron/stall behaviour may indeed induce a variable wing thickness after the design optimisation process.
In contrast, design of the stabiliser shapes is kept as simple as possible, to prevent unforeseen complications causing a fatal controllability issue. The major considerations in the design process are listed by Torenbeek section 9.5:

Stabiliser area, large enough for static and dynamic stability in all circumstances.
Aspect ratio, chosen such that the optimal lift-curve slope is used. Similar to main wing considerations, except sometimes in out-of-trim conditions.
Taper ratio. Moderate taper is usually chosen to save some structural weight.
Sweep angle. For high subsonic aeroplanes, the sweep angle and thickness ratio are chosen such that at design dive Mach number strong shock waves are not yet formed.
Airfoil shape. Must have a high $C_{Lmax}$ and large range of useful angles of attack, such as produced by symmetrical airfoils with thickness ratio between 9-12% and a large nose radius (NACA 0012).
Dihedral. To keep a large useable range outside the engine slipstream.

So design choices for the stabilisers are made such that the focus is on simplicity and functionality. A simple construction is less expensive, and less subject to manufacturing tolerances.


text:
When is Vmo/Mmo applicable?
I have read that for most planes Vmo (maximum operating speed) is the limitation below 25000ft and Mmo (maximum operating Mach number) is the limitation above 25000ft. Is it correct to say this and, if not, how would you explain this correctly?

The limitation is always the lower one of the two, meaning your actual IAS must be below Vmo and your actual Mach must be below Mmo.
Let us consider this case: you accelerate all the way to Vmo and climb at that fixed IAS. Two things are happening now:

The TAS is increasing because the air is getting less dense.
The speed of sound is decreasing because the air is getting colder (speed of sound in an ideal gas is proportional to the square root of the temperature).

Both of these effects result in an increasing Mach number (M = TAS / speed of sound). Eventually, the Mach number will reach Mmo and now you are limited by Mmo rather than Vmo. At what altitude this happens depends on the exact values of Vmo and Mmo and also on the actual environmental conditions (e.g. temperature).
As an example, let us consider a Boeing 737NG in ISA conditions with a Vmo of 340 kt and an Mmo of 0.82 (source). Then Vmo and Mmo will be equal at an altitude of 23711 ft at a TAS of 496 kt.

Thanks. So the altitude ranges given in the type certificate data sheet for VMo are then the ranges at which VMo is the lower one of the two?

@stevederekson555 Yes, but only in ISA conditions. A different temperature can slightly change that value.


text:
How to calculate density of ISA+10ºC at 11705m?
I know how to calculate the density under normal ISA conditions at a given altitude, but I'm unsure about how to go about calculating it at ISA+10ºC, or at any ISA+XºC conditions.

Do you know how to calculate (or get from the standard table) the pressure? Density is calculated from it and the temperature. Check Density of air.

at a pressure altitude of 11705 m or a geometric altitude of 11705?

Just going to answer my own question here, I found a very simple solution.
ISA + X ºC changes only the temperature. Pressure is ISA, because the model is static. So calculate ISA pressure with standard ISA formulae, calculate ISA temperature, add 10ºC, and obtain density through ideal gas equation. The ISA model presupposes that air is an ideal gas anyway.

Yep, they may use Kelvin for that application.  Seeing similarities to Clausius-Clapeyron equation.


text:
Does ADS-B signal contain the aircraft type?
I am working on the construction of an atmospheric model that calculates GHG emissions from aviation transport in France, as input I need an aviation traffic report as well as information on the type of aircraft (e.g Airbus A380).
To get this information, I am going to 'build' an ADS-B ground station, but I am wondering if the aircraft type information is included in the ADS-B signal?

Why not use a source like ADSBexchange or OpenSky that already collects the data you need? No need to reinvent the wheel.

Yeah really, reinventing that wheel would be like 95% of the project.

Related: How to get registration from ICAO 24 bit code?. Would Eurocontrol unique dataset for researchers of 12 million commercial flights database help?

Is a question of budget, as the project is being leading by a startup with commercial objectives, so no way to apply for a research quotation.

@MigueL: "no way to apply for a research quotation", I don't know if you're answering my comment, if yes, then you may see this database if open data, released each quarter since several years.

No, the airplane type is not in the signal.  The identification contains the ICAO 24bit (Mode S) code.  You then need to map that to a registration which will have the type.  As mentioned in the comments, services like ADSBexchange and OpenSky attempt to do that mapping as part of their information processing.
So if you extracted ID 0x4840d6 from the message, you could do a lookup to find it's registered in the Netherlands as a Fokker F70.


text:
Why are the grid fins on Starship pointy and sharp?
The grid fins on Starship are serrated, why? Does it help in transonic maneuvers?

Source: Starbase Factory Tour with Elon Musk [Part 1], YouTube, at 30:28

Maybe Elon's having Fred Flintstone over for dinner later and needs to tenderize a couple tons of brontosaurus steak?  Anyway, welcome to Aviation.SE -- please be sure to take the [tour] and read over the [FAQ] to get a better idea how Stack Exchange sites work.

Wouldn't this be a better fit on Space.SE?

@RalphJ It's specific to the aerodynamic reasons for this shape, which affect only atmospheric operation.  Firmly in a gray area, IMO.

@RalphJ For questions about the rocket, I would agree. But since this is about the aerodynamic design of the grid fins, I think the question also fits here.

Well those fins are useless in space, and they are an aerodynamic apparatus used to guide flight, so definitely a question best suited here.

Wow, the photo really drives home how huge the rocket is.

@Michael It's funny, but I was just thinking the exact opposite. It's perspective of time, in my case, I suppose. As a kid I built Apollo rocket models to better visualize the launches I was watching on TV. As far as VtC, Jpe61's comment here says it all for me. VtLO

@CGCampbell: For me the thing is that the rocket just looks incomprehensibly huge when put next to humans. But then you put humans next to the grid fins (which don’t look very big when attached to the rocket) and suddenly realize that even those are already huge.

Note that those grid fins are for Super Heavy, not Starship. Starship doesn't have grid fins, its aerodynamic control surfaces are flippety-flappety-bits. Unless you mean "the Starship system", which consists of Starship and Super Heavy.

Such design, with hyperbolic leading edges, has been invented by MBDA (Airbus branch for missile systems) represented by BAE Systems (defense contractor), and is described in the European patent 3 599 442 A1 filed on July 2018:

The curve helps reducing drag, especially at supersonic velocities, an important factor for missiles and rockets, for which fuel is very limited.

Having a hyperbolic curve for the leading edge
planform shape provides for a lower drag, in particular a lower wave drag. This means that the grid fins could be used as efficient lift and control devices/surfaces for supersonic
flight vehicles.

Fins in place at the top of a 70 m-tall Super Heavy Booster 4:

Source
The booster is used for the SpaceX Starship program. Curved leading edges are pointing at the ground, in the position required for booster return to its launchpad (video of the return trip). Fins are indeed used for the atmospheric flight. In space attitude is controlled using thrusters or reaction wheels.

Since those fins are used in the descent phase, isn't it counter-productive to minimize their drag? After all, the rocket needs to decelerate when those fins are deployed.

@PeterKämpf: They are not used to decelerate, but to maintain the stage vertical for engine efficiency. The engine is used for deceleration.

Yes, I understand that. But if they produced more drag, less engine fuel would be needed.

@PeterKämpf: My assumption is that it's more efficient to have the engine burning in the right direction than to try to add some deceleration with the fins, at the cost of having them less reactive, so having a thrust vector component perpendicular to the desired deceleration axis, and burning more fuel, which is very limited. Just a guess. Note the first use of curved fins is for missiles, this use here is a second application.

I'm guessing if they were mere paddles the steering/guidance behaviour would be poor at best (turbulence and such), and maybe somewhat unpredictable. Obviously this is a tradeoff between guidance and braking, and braking lost. Probably the fuel lost in braking was less than extra fuel needed for stabilizing flight with inferior fins (or paddles)

I see Mins was faster writing this

@PeterKämpf: A booster doesn't go straight up, it goes quite a long way down range.  If you want it to fly back to the point of origin, minimizing drag means less fuel needed for the flyback, so more can be devoted to launching payload.

Minimising drag also minimises friction. Originally SpaceX’s grid fins were made of aluminium which on its own couldn’t survive without an ablative coating. Newer fins were subsequently changed to titanium which doesn’t need the coating, but I imagine that you’d still want to reduce heat if you’re planning to reuse them many times.

@RobinWhittleton  "Minimising drag also minimises friction" - was that just clumsy wording or are you indeed trying to say that drag <> friction ?

Clumsy wording. My point was that more drag leads to more heat in the material.

I think the main issue is heat. Grid fins are made of titanium to keep from melting. More drag makes this more difficult.

@EricS: I understand Super Heavy's grid fins are actually steel.

@FredLarson True, they're titanium on Falcon 9. The issue of heat is still the same.

@RobinWhittleton, reentry heating mostly isn't from friction, it's from compression of the air.  If you want to minimize heating, you need to maximize drag, which lifts the compression shock wave off the surface of the rocket and causes it to heat the air instead.  See https://en.wikipedia.org/wiki/Atmospheric_entry

Edges like these reduce drag. They originated on Falcon9, where they fold away on ascent and fold out on return.
BUT, on Starship they don't fold away, saving the mass of the folding mechanism AND incurring the drag of flat edges on the way up.
@ElonMusk. Rotating the pointy edges to face upwards during launch will likely save drag on the way up too. Then rotate them down at the azimuth for return.
Alternatively, sharpen the top edges the same, to cut both ways and maybe even save more mass? Then if the drag on the way up is reduced, might that imply a reduction in the mass of the mount-points as well?
Afterthought.
Boosters will be reused a lot (maybe 100 x). (Mass and drag) saved by booster optimization will yield mass-to-orbit scaling of the product: (#launches x #boosters). Seems worth it.

Wouldn't rotating the fins just 90 degrees (facing up the narrow edge) on the way up save even more drag? Or am I missing something?


text:
Aircraft with large, double orange lights at night
Question:
I saw an aircraft flying over, about two hours after sunset with a pair of bright, large, constantly on, orange lights. I'm wondering what kind of aircraft this could have been.
More details:

Latitude - Longitude: 43.1, 25.4 (central Bulgaria)
Date: 8 August 2021
Time (approximately): 22:30 EEST (Sofia, Bulgaria)
Estimated direction: flying from NNE to SSW
Estimated height: unsure, but I'm guessing at least several kilometers up (see below)

Additional information:
We were stargazing with a group of adults and children, looking north towards the Perseus constellation, looking out for meteors from the Perseids meteor shower.
At some point we saw two bright orange lights approaching from the north at a constant speed. They were not blinking, but permanently on. They were also quite large (not the blinking green/red dots I'm used to seeing on airliners). And we could see them as round shapes, much bigger than stars or planets, but much smaller than the moon. They appeared about the size of the tip of a pencil eraser. The craft passed straight overhead and then continued flying in a straight line until it disappeared out of sight. I estimate we were able to see it for at least a minute. We were able to see a good portion of the night sky from our location, I estimate at least 120 degrees. We didn't hear any sound coming off it and with the naked eye there were no other lights. However, looking with binoculars, a regularly flashing white light was visible between the orange lights. This light was set a fraction to the rear of the craft, but more or less between the orange lights.
The orange lights appeared to me as circles all the time, while the craft was coming towards us, while overhead, and while flying away from us. So in my mind they must have been sphere shaped.
I checked where the ISS was at that time with this ISS Tracker and it appears that was above northwest Australia, so nowhere near.
What kind of aircraft could this have been?

related: https://aviation.stackexchange.com/questions/63851/what-type-of-aircraft-would-fly-with-an-orange-light-at-night

Aircraft do not have blinking green lights. Not if they are functioning properly at least :) Blinking lights are either red (beacon) or white (strobe).

@Jamiec - thank you. Yes I'd seen and considered that question and its answers, but none seem satisfactory.

@Jpe61 - thank you. So the green lights are always static? I didn't know that. Thanks.

Yes. Typically aircraft have three types of lights: static (always on) nav lights: red shown to front and left, green shown to front and right, and white shown to rear sector. Beacon: a blinking (or rotating type) red light shown to all directions. This/these are kept on when engines are running, or plane is about to start. Strobe light(s): high power white blinker light shown all direction. Strobes are the most visible light, can be seen from great distances (>100km). Typically switched on when entering the runway for takeoff, and shut off when taxiing off the runway after landing

... and of course landing- and taxi lights, which are self explanatory. Is it possible you saw a plane approaching an airfield for landing? The lights might have been landing lights? Some planes have multiple landing lights, in wings for example.

Thank you for explaining @Jpe61. I know a bit more about aircraft lights now. The one I saw didn't have any red or green lights (that I could see at least). With the naked eye I only saw the orange lights at the sides (I'm assuming these were at the sides - at the ends of the wings, but I couldn't see the actual aircraft, so not certain) and no strobe light. With binoculars I did see a strobe light that appeared to be in the center of the aircraft (on the underside). I also didn't hear it, which all suggests the aircraft was very high.

I looked up the nearest airfields. There are some small ones around, but quite far away. One about 50 kilometres to the northwest. Another about 20 kilometres to the east. And a third one about 40 kilometres to the south. This is new territory for me, but to me the aircraft seemed to be cruising.

I'm kinda veering in the direction of this being some sort of a drone.

@Jpe61 Hmm, yes perhaps. What would be your thinking behind it? And 'some sort', what kind of type/purpose would you think?

Just the fact that if it was a legitimate "real" acft, it would have had the standard light setup. There are no exception to that.

If a multi-rotor drone had amber LEDs on two of its rotors, that would explain why the lights appeared basically circular to observers throughout multiple viewing angles. And drones are quiet, and their height would be very difficult to gauge at night.

Thank you @ CCTO, that makes sense. I've been looking into drones and there are so many types; I had no idea. @Jpe61's suggestion that it was some sort of drone starts to make sense. From the size and the distance it travelled I'd think it would have been a commercial or military drone. No idea why it would have those orange lights though. And also, if drones fly around like that wouldn't it be good if they had the same navigations lights as airplanes?

@CCTO -- are there any known examples of multi-rotor drones with lights on rotor tips?

Could this have been some sort of craft based on two balloons?  Maybe even two "fire balloons" joined together with a light between?

Re "From the size and the distance it travelled I'd think it would have been a commercial or military drone. " -- on clear nights (and note that the OP was stargazing) an inversion layer often sets up in the lower atmosphere, inhibiting mixing and allowing there to be strong winds aloft, but little or no wind at the surface.  Hence a balloon just a few hundred feet up could travel much faster than you might expect based on the wind felt at ground level.

The large size of the orange lights you saw-- "much bigger than stars or planets"-- suggests two fire balloons joined together, with a blinking white light between.  The lack of sound is also consistent with this.  For a powered aircraft to be flying so high that you couldn't hear the engine, and the lights to still appear "much bigger than stars or planets" from your vantage point, the lights would have to be enormous, which is implausible.
Note that on clear nights, a temperature inversion layer often sets up in the lower atmosphere, inhibiting mixing and allowing there to be strong winds aloft but little or no wind at the surface. Hence a balloon just a few hundred feet up-- or a few thousand feet up-- could travel much faster than you might expect based on the wind felt at ground level.

This sounds like a plausible explanation, but I have a few questions about it. The page you shared talks about using candles for the balloon, which would cause the air in the balloons to heat up. If candles were involved I'd expect some flickering in the lights, which I don't remember seeing. Although, if a prankster had made this and put a white flashing light in the middle, they could have also made larger lights at the sides. Also, it was going in such a straight line - like a ruler. Wouldn't you expect wind to cause some lateral movement? I appreciate your thoughts.

@Dvaeer If what you saw was indeed two fire balloons, then they would have been completely still relative to the air, so there would be no relative wind to make them flicker. Likewise, their direction of motion would have been directly in line with the wind, so unless the wind suddenly changed for some reason, their flight path would be a straight line.


text:
Why are there two local maximums on some CL vs AOA curves?
I know what a stall is but I don't understand why there are in some cases two local maximums on the $C_L$ vs AOA curve of some airfoils. What is the reason for the mini stall that occurs before the main stall?

Note that the plot is up to 90°, which corresponds to the aircraft flying with the nose pointing straight up—or the aircraft falling straight down with the nose horizontal.

The mini stall is the stall that we normally talk about when considering the flight of an aeroplane, and is therefore the main stall. Below the AoA where the first stall occurs, the wing profile is reasonably aligned with the airflow, and flow at the upper wing surface can remain attached. When upper surface flow detaches:

upper surface suction force decreases, causing the "mini-stall";
air resistance rises dramatically due to the stalled upper surface flow;
lift is still generated by the lower surface deflecting the airflow downwards, like a flat plate does.

So beyond the normal range stall the wing still generates lift, and increasing AoA produces even more lift. The reason why aeroplanes cannot fly in the region beyond the first stall can be found from considering aerodynamic drag as function of AoA as well.

From this answer: $C_d$ of a NACA 0012 profile staling at 11º. The jump in drag is dramatic, and would usually be impossible to compensate for with engine power. Drag is the reason why we want to remain at low wing AoA.

Also, below the main stall the flow is behaving in a linear way. Above, nonlinear behavior, resulting in positive damping, can ruin your day.

Thank you so much!


text:
Wing and horizontal/vertical tailplane airfoil type and relative thickness?
I've been searching for data on the airfoil type (namely if they are supercritical, aft-loading etc.) and relative thickness (average or in different positions) of the empennage (both horizontal and vertical tailplane) and wing of the following airplanes:
A320/A319, B737, A220/Bombardier C Series , E195-E2.
I've found data on the A320's wing (was unable to find data on the other wings), and no data on any of the empennages. I've checked Jane's, Thorenbeek, APM's etc. Where can I find this information?


text:
Length from nose to end of flight deck / start of cabin?
I'm trying to estimate this length for the A319-100, B737-700 and A220-300. It is not easy using the drawings, because many cabin drawings don't include the flight deck. I know that it is established by law that this distance is minimum 4m.
Does anyone happen to know what these distances are? Perhaps there are pilots here familiar with cockpit dimensions.

"I know that it is established by law that this distance is minimum 4m." -> Could you link that law? I've never heard of that and it sounds a bit weird.

This document has extensive drawings and dimensions but I haven’t found the one you are looking for. However given the mid-point of the front door is 5.02 m from the cone, the door is 1m wide (so take out 0.5 m), and there’s the lavatory between the cockpit and the door there’s probably just under 4 meters.


text:
How is a design cruise altitude picked?
Different planes have different design cruise altitudes, given by the manufacturer. You can find these in their Airport Planning Manuals or in Jane's All the World's Aircraft. I know that the first iteration of these values is usually picked after designing the fuselage, and before designing the wings and other elements.
What is this decision based off? Is it that a larger frontal fuselage surface merits a higher design cruise altitude to reduce pressure drag? What considerations do you think are important to make at this stage in the design process?

Does this question help?

Yes, that answers the question. It's clear then that it's a weight issue, you estimate the aircraft weights and using that data you estimate a cruising altitude.


text:
What are typical values for CLmax in clean configuration?
I know typical cruising CL tends to be in the range of 0,5. Maximum CL I'm guessing around 1. Does anyone know typical values?

More like 1.3 to 1.6.  Don't have a source so can't post as an answer.  If you used 1.5 you'd be in the ballpark for the vast majority of cases.

@JohnK Is this the same for planes that use supercritical airfoils? These usually stall for lower AoAs I believe.

I would say so. SC airfoils typically have laminar separation bubbles at the LE, due to the sort of squared off nose curvature, that cause them to let go from the LE instead of the TE, but the AOA this occurs is still up there. I dimly recall that the SC airfoil of the CRJ stalled at about 14 deg, and the pusher fired about a degree or two below that. because when it went the entire wing stalled at once. Frosted wings would drop the stalling AOA down to about 9-10 deg, well below pusher and there have been a number of crashes of Challengers and CRJ200s from morning frost + aggressive rotation.


text:
What chord should I use to calculate Reynolds number?
Mean geometric chord of exposed wing, or mean aerodynamic chord of gross wing? It's not particularly clear in the literature.

Reynolds number is a variable parameter. There are multiple definition and you can use one of the two MAC, the important thing is that you specify the reference of your calculation. Usually between MAC of gross and exposed wing it would not change a lot(I would expect 10% changes), and seen that we are speaking of the order of magnitude of at least 1*10^6 for a commercial aircraft wing, the changes are negligible.
Moreover, Reynolds number must be read with respect to the particular phenomenon you are using it for. For example as a reference value for a transition computation from laminar to turbulent on the wing, I would use MAC of the exposed wing, it would seem to me more appropriate seen that the gross one have a strong interaction with the fuselage.

Depends on what you are trying to accomplish. If you are comparing different aircraft, it probably doesn't matter as long as you always do it the same way. If you are designing a wing, the exposed area is what matters. If your wing has taper, you might want to determine the number at multiple points as the tip will be lower than the root, and might be able to use a different airfoil.


text:
Does the Prandtl-Glauert correction use the airplane's Mach number, or its effective Mach number corrected for sweep?
The Prandtl-Glauert correction adjusts the lift curve slope of an airfoil to different Mach numbers. Should the Mach number of the airplane be used or the effective Mach number that the leading edge of the wing sees, namely $M\cos(\Lambda_{LE})$.

As far as we are considering the airfoil, it depends which profile do you take. In other words you have to take always the Mach considered in line with the chord of the airfoil.


text:
Does the A220-300 have krueger flaps or are all of its leading-edge highlift devices slats?
They look like slats to me, but I could be wrong. I'm asking because I know the 737, a very similar airplane, has inboard krueger flaps.
Also, what number of slats/krueger flaps does it have?

All are slats. Here is one taking off. and a better view of one in the air. It looks like there are as many as four sections but they all extend and retract together.